This application proposes to identify which synapses are involved in phased synaptic remodeling. By quantitative ultra-structural morphometry and synapse counts, the effects of ovariectomy (low estrogen), progesterone, and ring A-reduced androgens will be studied. Freeze-fracture analysis will be used to determine whether intramembranous protein particle(IMP) deletion regularly precedes synaptic changes and whether there is a critical level of IMP density in postsynaptic membranes below which it is not possible to maintain cyclic circuitry. Neuronal proliferation and differentiation in fetal hypothalamic cell cultures will be studied utilizing cell- and molecular biology methods to probe the appearance of oncogenes and intracellular/membrane proteins.